The invention relates to the utilization of foam processes for making non-woven webs using particular raw materials, and for making particular end products. Foam processes are basically as described in U.S. Pat. Nos. 3,716,449, 3,871,952, and 3,938,782 (the disclosures of which are incorporated by reference herein), and in pending U.S. application Ser. No. 08/923,900 filed Sep. 4, 1997 and U.S. application Ser. No. 09/098,458 filed Jun. 17, 1998, the disclosures of all of which are also incorporated by reference herein.
Foam processes are normally used for making planar forms having a uniform thickness, i.e., two-dimensional shaped forms, during web formation. In accordance with the present invention, a three-dimensional shaped form is created by using a three-dimensional mold during web formation from one or more foam layers. Using a three-dimensional mold, e.g., a wire mesh mold, a pleated or grooved filter product, for example, can be formed directly from a foam having fibers or particles which, when applied to the mold, form the product. A wide variety of products can be produced using the foam processes and three-dimensional molds disclosed herein. For example, three-dimensional molds and foam processes are useful to produce a wide variety of filter products, including automotive pleated fluid and air filters, pleated heating and/or air conditioning (HVAC) filters, shaped breathing mask filters and bacterial filters, laminated cleaning products with super absorbent middle layers, such as a mop wipe shaped to fit a cleaning mop head, and other products.
The present invention can be used to eliminate subsequent mechanical pleating steps or milling steps previously used to create pleats and grooves in a two-dimensional planar web sheet created using two-dimensional planar molds and foam processes. In particular, the present invention obviates the prior art process of mechanically cutting grooves and other shapes to form a three-dimensional planar-shaped product after it has been formed using foam processes. The present invention avoids the prior need for process equipment that shapes the substantially planar intermediate web products formed from two-dimensional molds into a three-dimensional final product. The present invention is particularly suited for use in production of pleated and grooved filter papers, especially those having applications in automobiles.
The foam process of web making is used for making products, e,g., webs using particles or fibers, e.g., short cut fibers, synthetic fiber materials, fibers from mechanical cellulose wood pulp or chemical cellulose wood pulp, or other web materials. Utilizing the foam process, it is possible to produce three-dimensional, non-planar webs from a variety of fibers, particles or combinations of fibers and particles.
One application of the invention relates to the production of pleated or grooved filter paper, particularly for automotive use. Filter paper started to be used in automobiles some 40-50 years ago, and today is standard equipment in every car with a combustion engine. The applications for filter papers today can be divided into the following grade categories: auto air, oil, heavy-duty air (HDA), fuel media, and cabin air. The auto air media/filter paper is designed to trap the particles entering the engine with the air. The HDA filter paper has the same function, but is designed for a more demanding environment with large amounts of dust in the air (e.g., earth moving machines, etc.). An oil media/filter paper is designed to take the particles out of the oil stream entering the engine. The fuel media/filter paper is designed to filter particles from gasoline or diesel fuel before it enters the engine. The cabin air media/filter paper is designed to trap the outside particles before they come into the cabin or compartment where the passengers are sitting. There are also other applications for such filter papers.
Automotive filter papers have previously been produced according to wet-laid processes, which date back to the early part of the 1900s. In the wet-laid process, fibers are broken up under agitation in a pulper. The fibers are then pumped in a liquid slurry through deflakers and refiners to the paper machine. The deflakers and refiners disperse the fibers, and give them a better surface for generating bonding strength. The main components on the paper machine are the wet end and the dry end. Between the pulper and the wet end, various types of wet and dry strength enhancing chemicals are also added. The wet end comprises a headbox and dewatering elements. Typically the headbox has a flat fourdrinier, incline wire, or cylinder type foraminous element. The dewatering elements are designed to suck out water from the slurry to dewater it from roughly a 0.05% fiber consistency to a 25% fiber consistency on a moving wire (foraminous element). After the wet end, the media enters the dry end. The objective there is to dry the filter media from 25% to about a 98-99% fiber consistency.
The filter media is now either impregnated xe2x80x9con-linexe2x80x9d on the same paper machine, or rolled up and impregnated xe2x80x9coff-linexe2x80x9d on a separate impregnation machine. The objective of the impregnation process is to fully saturate the media with a resin or latex (thermosetting or thermoplastic), and thereby give the media its final mechanical strength as well as making it convertible into a filter. The impregnation process basically includes an impregnation unit followed by dryers. The impregnation unit can be a size-press, roll coater, curtain coater, or the like, and the dryers can be any conventional contact/non-contact types. When the media reaches about a 10-15% moisture content, the oil and HDA media types are grooved, giving them a continuous S-shape in the machine direction. Grooving the media type increases the overall filtration surface and helps keep the subsequently formed pleats separated when pleating the media and building the filter element.
After impregnation the media is slit into various slit width sheets before packaging and sending to a customer. At the customer site, the media is mechanically pleated on conventional pleating machines giving the media its final physical configuration before building a filter element containing the filter paper. How the ends of the media are sealed, the media further polymerized, and which characteristics are particularly important, depend on the customer and end application, and these details are conventional.
The process of the U.S. patent application Ser. No. 09/098,458 discusses the manufacture of a planar sheet of filter paper by means of the foam process, and then subsequently the sheet is grooved and pleated to make the actual filter material. The present invention forms the filter paper on a mold, which is grooved, pleated, or grooved and pleated itself. There is no need to perform subsequent mechanical steps of pleating, grooving or otherwise imparting three-dimensional shapes to the web product extracted from the molding process.
Forming products from a fiber or particle foam is advantageous over wet-laid processes. For example, filter paper has been manufactured using a water-laid process. In that process, fibers in a liquid suspension are introduced onto a grooved mold. The depth of the liquid slurry is relatively shallow. Soon after the introduction of the fiber suspension, the slurry surface sinks below the top portion of the lower mold, losing the hermetic seal permitting suction from beneath the mold to avoid removing water from the fibrous slurry. When the seal is lost, the suction acts primarily on the portion of the mold having no contact with the suspended fibers. Consequently, the fiber formation at the bottom of the mold is slow and not optimal. Additionally, there is a possibility that the top portions of the mold would collect a smaller number of fibers than the bottom portions, because the fibers in the liquid slurry tend to settle and concentrate at the bottom of the mold. In contrast, the foam processes disclosed herein involve one or more layers of foam that each form a relatively-deep layer of foam in a three-dimensional mold. Because of the depth of the foam, it is unlikely that the upper surface of the foam will sink below the peaks in the lower mold surfaces. In addition, an upper mold may be used to shape the upper surface of the foam so as to conform to the shape of the underlying lower mold, and thereby avoiding having the tops of a lower mold extend entirely through a foam layer.
Another problem exists with wet-laid processes if the filter paper is manufactured using several different layers, materials, substrates, or combinations thereof. While being introduced on a previous layer (or layers) in dilute suspensions, subsequent layers tend to orient the fibers from a previous layer in the bottoms of the grooves. This causes the final product to have an uneven thickness, which in turn causes a decrease in filtering ability. Foam processes are better suited to layering different foams, where each foam layer has a different consistency of fibers or particles. The foam layers tend to retain randomly oriented fibers, which is often desirable. Alternatively, the fibers in the foam can be oriented parallel to the flow path in the foam injection nozzle. By injecting the foam into the mold vertically from the nozzle, it is possible to preserve the generally-vertical fiber orientation in the foam as deposited in the mold. The vertical fiber orientation in a final web product can be beneficial to form relatively-thick webs and relatively-porous webs.
In these prior art wet-laid and foam processes, there are potential problems caused on the one hand by forming in wet-leid processes, and on the other hand by pleating and grooving the filter paper separately in foam processes. First, increasing process steps cause higher manufacturing costs. Combining several process steps into one, the overall process becomes shorter and, consequently, less expensive. Second, mechanical changes to the formed filter paper may decrease the durability of the final product. Bending a formed planar filter paper to form pleats and grooves creates stress to the bent portions, and that stress may reduce the quality of the final product through rapid deterioration.
The present invention is a foam web manufacture process that uses molds to shape and dry the foam into three-dimensional products, such as three-dimensional filters. These products may be single layered formed from a single application of foam, or a laminate formed of several layers of different foams. In a simplistic description, foam comprises a slurry of air, water, surfactant, and fibers or particles. The type of fibers, particles, or combination of fiber and particles will depend on the product to be produced. For example, the fibers in the foam may be short cut fibers, having an average length of 0.05 mm (millimeters) or less. The fibers or particles conform to a three-dimensional mold as the foam is deposited in the mold. As the foam is deposited on the mold, the water and air (which is in the foam as air bubbles having a wide variety of different diameters) are drained through the mold, extracted and reused. The fibers or particles from the foam are deposited on the mold to form the web product. The fibers or particles are dried on the mold and the completed three-dimensional product is removed from the mold. The web product may be formed from a combination of fibers and particles, or entirely of particles that are deposited from the foam.
The introduction of the foam onto three-dimensional molds is performed in a careful manner, to prevent the problems experienced by the water-laid process. These problems can be prevented, in part, because the consistency of the foam is 1% to 10% (and can be 20% for foams with super-absorbent) fibers) and is higher than the typically 0.01% to 0.5% consistency of the slurry in the conventional water-laid process. As a consequence of the higher consistency, the use of the foam process permits formation of thicker products, such as thicker filter papers or thicker layers of paper in a single stage. If larger consistencies are used in liquid-laid processes, the fibers tend to aggregate and form flocs before web formation occurs. Floc formation decreases the quality of the final product because of the associated fluctuations in thickness and other properties of the filter paper, which in turn cause variations in filtering ability within the same product.
Additionally, the foam requires much less liquid than the liquid-laid process, reducing the water consumption significantly. A reduction in the water consumption decreases the size of equipment needed for transporting liquid downstream of the mold. After the foam is drained from the mold, the foam can be substantially reused. Generally, only fibers and particles, and possibly a surfactant, are added to the reused foam before it is deposited in another mold.
In one embodiment, after foam is introduced onto a bottom mold, a complementary top mold is placed on top. Preferably, the top mold is substantially the inverse of the bottom mold, such that the ridges of the top mold substantially fit in the grooves of the bottom mold. Similarly, the grooves of the top mold fit substantially around the ridges of the bottom mold. The top mold can be used to ensure that the top portions of the bottom mold are covered with foam and thus sealed. Ensuring that foam remains over the top portions of the bottom mold prevents the loss of the seal and the associated problems with suction described above. Additionally, the top mold can be used to apply pressure on the foam, increasing the pressure on the top surface of the foam and assisting the removal of foam from the filter layer.
After the filter layer is substantially formed, the top mold is removed and the filter paper can be either taken to the drying phase or taken to a phase wherein another layer of foam is deposited. Although substantially the same foam material could be deposited using a new headbox in the manner described above, a different foam material can be deposited. Additional layers, for example three or more layers, could be deposited on the formed layers. The number of potential layers is determined partially by the desired properties of the final product.
In another embodiment, the production machine is a batch-type machine, wherein each batch contains at least one bottom mold. For each batch, there is a trough, which contains, for example, five rows and five columns of bottom molds. After the desired amount of foam is deposited using a headbox on the bottom molds in the trough, an insert containing a matching number of top molds is placed on top of the foam. That trough and insert move down the production line, and an empty trough begins the batch process anew.
In another embodiment, the production machine is a continuous-type machine, wherein the bottom and top molds are incorporated into a moving wire, which is also called a foraminous element, and roller system. The bottom mold moving wire contains repeated bottom molds, such that as the bottom mold moves, e.g., laterally or rotationally, new bottom molds are exposed to the headbox. Similar to the batch process, the headbox deposits foam on the bottom molds mounted on the bottom mold moving wire. Thereafter, a complementary top mold attached to a top mold belt is placed on top of a corresponding bottom mold containing foam.
In a further embodiment, after a layer has been formed, the mold is opened. A similar procedure to the ones described above may be done such that another layer is formed. Alternatively, the recently formed layer, or layers, may be run through a blow-drying oven or similar equipment to aid in the drying process.
In yet another embodiment, multiple discrete layers of foam are deposited on the bottom mold before the top mold is placed on top of the foam. After deposition of each layer of foam, some foam may be drawn through the bottom mold without placing the top mold on top. Removing some foam may both ensure the foam maintains a reasonable height in the mold and reduce the overall process time. Alternatively, foam removal may occur after all layers have been deposited. In this embodiment, the top mold is useful when the height of the foam is less than the height of the bottom mold. In such circumstance, without a top mold the seal might be lost if a gap in the foam forms as the top portions of the lower mold extend up through the foam. The top mold prevents gaps in the foam by pressing the foam down into the lower mold, evenly distributing the foam in the lower mold and ensuring that the foam layer maintains a uniform thickness. A top mold is also advantageous to provide better drainage of the foam by adding pressure that forces the foam through the lower and upper molds, which are typically a wire mesh.
In a further embodiment, the foam layers are deposited in a quick sequence in a mold without a large time delay between layer depositions. For example, this can be done using multiple headboxes, each headbox depositing different foam with independent properties. Alternatively, this can be done using a single headbox with the capability of depositing different foams with independent properties. In the second example, the independent foam layers are still deposited sequentially, but the same headbox is used for all layers.
There are multiple advantages to using the present invention, and the following is a non-exhaustive list of benefits. First, the process is relatively fast, and delicate or reactive substances, like active carbon, odor removing substances, salts, super-absorbent products, etc., may be used without substantial degradation or substantial loss of properties. Second, the process can be operated in either batch- or continuous-type machines, providing flexibility in equipment or plant design. Third, the process uses foam, which provides the ability to deposit multiple layers without mixing different layers. Fourth, the process obviates the need to groove or pleat the filter paper after formation. Since the paper is not subjected to bending after formation, the risk of breaking the filter layers is minimal. Fifth, the process is useful with any short fiber, e.g., fibers of 50 mm or less, such as synthetic fibers, mechanically-treated wood pulp or chemically-treated wood pulp.
The present process has advantages over thermo-forming techniques used for shape filters. Thermo-forming is a post mold process to shape a filter element. Thermo-forming processes are unnecessary with the present invention that shapes a filter element using the same mold in which the fibrous foam is solidified into a three-dimensional fiber element. In addition, the foam used with the present process produces a more uniform filter product than does the wet-laid or dry-laid fiber processes typically associated with processes involving thermo-forming. However, thermo-forming can be used on the web product extracted from the mold and produced with the present invention.
While the present invention has been described in connection with the production of filter papers, the invention may be used to manufacture other three-dimensional products using foam. The present invention offers other advantages, which will become apparent to a person of ordinary skill in the art when considered in connection with the accompanying drawings.